1. Field of the Invention
The present invention relates to an image forming apparatus capable of retracting a image writing unit that includes an optical system unit containing optical components from a write position to a retract position, and a holding unit supported by a supporting unit while holding the optical system unit in a movable manner.
2. Description of the Related Art
Such an image forming apparatus is known as described in, for example, Japanese Patent No. 2849978. The image forming apparatus holds, on its opening and closing door that opens and closes a maintenance opening of a chassis, a image writing unit that writes a latent image to a image carrier such as a photosensitive element by scanning with write light. By retracting the image writing unit from inside the chassis according to opening of the opening and closing door, a processing unit that has been hidden behind the image writing unit is exposed. With this structure, the image writing unit is pulled out of the chassis according to opening of the opening and closing door, and the processing unit is exposed out of the maintenance opening, providing improved maintenance. Besides this structure, the detachable image writing unit exposed to the outside may be pulled out from the maintenance opening as necessary, so that devices having been hidden behind the image writing unit are exposed. The maintenance can be improved even with this structure.
On the other hand, the optical system unit of the image writing unit easily degrades write accuracy due to temperature increase. When the temperature in the apparatus increases as a rotating polygon mirror for deflecting the write light is driven, a lens and mirrors are thermally expanded, causing the light path of the write light to slightly fluctuate. In an image forming apparatus described in Japanese Patent Laid-open No. 2002-318522, an intake fan for taking the outside air into the chassis is coupled to an optical system unit through ducts, so that the optical system unit is cooled by airflow. At the connecting parts of the ducts and the optical system unit, the ducts cover the outer surface of the optical system unit, and the airflow inside the ducts cools the optical system unit while moving along and being in contact with the outer surface of the unit. The cooling can suppress degradation in write accuracy due to temperature increase in the optical system unit.
However, pulling the ducts in the chassis causes difficulties in downsizing the apparatus.
Cooling the optical system unit is possible without using the ducts, by fixing the optical system unit at the right front of the intake fan with, for example, a metal frame so as to receive the airflow directly through the intake fan.
In the image forming apparatus described in Japanese Patent No. 2849978 and those allowing their late image writing devices to be movable and detachable, use of such a cooling system has been difficult due to the following reason. Specifically, an optical system unit that performs light scan with a precise pitch such as a several tens of micrometer order is required to perform high-accuracy positioning in the chassis of the image forming apparatus. Thus, to allow the image writing unit to be movable or detachable, it is desirable to use an image writing unit capable of holding an optical system unit to be freely movable on a holding unit. This is because, when setting the image writing unit to its write position, the optical system unit can be positioned in the chassis by causing the optical system unit to freely move on a holding unit with its predetermined hitting portion hitting a blocking portion in the chassis. In this structure, however, the optical system unit is surrounded by the holding unit, causing difficulties in allowing the airflow from the intake fan to directly hit the optical system unit.